This invention relates in general to apparatus for converting thermal energy into mechanical or electrical energy and, more specifically, to an apparatus utilizing a small temperature differential between two liquids to produce work.
A very great many devices have been developed for producing electrical power, operate mechanical devices, etc. using a variety of energy sources, such as chemical energy, solar energy, temperature differences and the like. While many of these are very effective for specific purposes, there is a continuing need for improved efficiency and the ability to use heretofore untapped sources of energy.
One potential source of energy lies in the small temperature differences between liquids such as the difference between the higher temperature of water at the surface of a lake or ocean and the lower temperature at depth, the warmer water in a surface pond and the cooler water in a well, tanks at different depths in the earth, etc. While a number of devices have been developed to utilize these small temperature differences in producing mechanical or electrical energy, they tend to be complex, expensive for the amount of energy converted and to have low conversion efficiency.
One such prior device is the expansible/compressible container system described by Backlund in U.S. Pat. No. 4,341,075 in which an expandable container is alternately expanded and contracted by alternately introducing warm gaseous refrigerant and cool condensed refrigerant into the container. While operable, this arrangement produces relatively little mechanical energy and is mechanically complex.
A number of different generators have been developed based on the heat pipe principle, such as those described by Shina et al. in U.S. Pat. No. 4,546,608, and Pravda et al. in U.S. Pat. No. 3,429,122. Although heat pipes excel for certain purposes under a narrow range of conditions, such as heating and cooling of buildings in certain climates, they tend to be expensive, complex and inefficient under many conditions.
Closed cycle vapor engines, such as are described by Leffert in U.S. Pat. No. 3,670,495 have been developed for a number of purposes, but have not reached a level of efficiency justifying widespread use. Other systems utilizing small temperature differentials have been conceived, such as turbine system described by Pecar in U.S. Pat. No. 3,932,995, the solar powered turbine described by deGeus in U.S. Pat. No. 4,081,965, the low pressure engine of Siegel as described in U.S. Pat. No. 4,036,017, and the heat vapor bubble engine described by Schur in U.S. Pat. No. 3,916,626. It appears that none of these has achieved a level of economy and efficiency necessary for significant commercial applications.
Thus, there is a continuing need for improved energy conversion apparatus for converting small temperature differentials into useful work, either through mechanical or electrical means. In particular, improvements in initial cost of the apparatus, less mechanical complexity and higher energy conversion efficiency are needed.